Environmental Impact Of Aviation Research Articles

Examining Opportunities and Challenges for Addressing the Climate Impact of Aviation: A Narrative Review

Aviation is responsible for about five per cent of global greenhouse gas emissions through the burning of fossil fuels. This analysis explores the potential and obstacles of measures to reduce travel, energy use, and emissions in order to lessen aviation's impact on the climate in Sweden. Various efforts have been made to decrease aviation's climate impact, from regulations to alternative technologies for jet fuel. These efforts face multiple challenges, many rooted in social and political issues that are often overlooked in favour of technological fixes. One major hurdle is creating a market for alternatives to traditional jet fuel as consumer awareness and willingness to invest in these innovations remain limited. Current policy measures have proven ineffective at driving change; an understanding of aviation as a socio-technical system is essential moving forward. The significance of this review lies in its comprehensive examination of ways to diminish aviation’s climate impact, presenting new perspectives and identifying areas for further research by considering all components, their interactions, and interdependence.

Radiative Effect of Two Contrail Cirrus Outbreaks Over Western Europe Estimated Using Geostationary Satellite Observations and Radiative Transfer Calculations

AbstractEstimation of the perturbation to the Earth's energy budget by contrail outbreaks is required for estimating the climate impact of aviation and verifying the climate benefits of proposed contrail avoidance strategies such as aircraft rerouting. Here we identified two successive large‐scale contrail outbreaks developing in clear‐sky conditions in geostationary and polar‐orbiting satellite infrared images of Western Europe lasting from 22–23 June 2020. Their hourly cloud radiative effect, obtained using geostationary satellite cloud retrievals and radiative transfer calculations, is negative or weakly positive during daytime and positive during nighttime. The cumulative energy forcing of the two outbreaks is 7 PJ and −8.5 PJ, with uncertainties of 3 PJ, stemming each from approximately 15–20 flights over periods of 19 and 7 hr, respectively. This study suggests that an automated quantification of contrail outbreak radiative effect is possible, at least for contrails forming in clear sky conditions.

Hydrogen in aviation: A simulation of demand, price dynamics, and CO2 emission reduction potentials

Aviation contributes to anthropogenic climate change by emitting both carbon dioxide (CO2) and non-CO2 emissions through the combustion of fossil fuels. One approach to reduce the climate impact of aviation is the use of hydrogen as an alternative fuel. Two distinct technological options are presently under consideration for the implementation of hydrogen in aviation: hydrogen fuel cell architectures and the direct combustion of hydrogen. In this study, a hydrogen demand model is developed that considers anticipated advancements in liquid hydrogen aircraft technologies, forecasted aviation demand, and aircraft startup and retirement cycles. The analysis indicates that global demand for liquid hydrogen in aviation could potentially reach 17 million tons by 2050, leading to a 9% reduction in CO2 emissions from global aviation. Thus, the total potential of hydrogen in aviation extends beyond this, considering that the total market share of hydrogen aircraft on suitable routes in the model is projected to be only 27% in 2050 due to aircraft retirement cycles. Additionally, it is shown, that achieving the potential demand for hydrogen in aviation depends on specific market prices. With anticipated declines in current production costs, hydrogen fuel costs would need to reach about 70 EUR/MWh by 2050 to fulfill full demand in aviation, assuming biofuels provide the cheapest option for decarbonization alongside hydrogen. If e-fuels are the sole option for decarbonization alongside hydrogen, which is the more probable scenario, the entire hydrogen demand potential in aviation would be satisfied according to this study's estimates at significantly higher hydrogen prices, approximately 180 EUR/MWh.

Powering aircraft with 100 % sustainable aviation fuel reduces ice crystals in contrails

Abstract. Powering aircraft by sustainable aviation fuels (SAFs) is a pathway to reduce the climate impact of aviation by lowering aviation lifecycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100 % SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between the Deutsches Zentrum für Luft- und Raumfahrt (DLR), Airbus, Rolls-Royce, and Neste, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100 % HEFA-SPK (hydro-processed esters and fatty acids–synthetic paraffinic kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56 % reduction in ice particle numbers per mass of burned fuel was measured for 100 % HEFA-SPK compared to Jet A-1 under engine cruise conditions. The measured 35 % reduction in soot particle numbers suggests reduced ice activation by the low-sulfur HEFA fuel. Contrail properties are consistently modeled with a contrail plume model. Global climate model simulations for the 2018 fleet conservatively estimate a 26 % decrease in contrail radiative forcing and stronger decreases for larger particle reductions. Our results indicate that higher hydrogen content fuels as well as clean engines with low particle emissions may lead to reduced climate forcing from contrails.

Optimal Sizing of Fuel Cell and Battery in a Direct-Hybrid for Electric Aircraft

The climate impact of aviation can be reduced using powertrains based on hydrogen fuel cells and batteries. Combining both technologies in a direct-hybrid without a DC/DC converter is a promising approach for light-weight systems. Depending on the power demand, both the fuel cell and battery are used to provide power or only the fuel cell is connected to the powertrain. The system voltage in a direct-hybrid is determined by the fuel cell and battery, but the performance of fuel cells is affected by low-ambient pressure at high altitudes and the battery voltage is affected by state of charge and discharge rate. Taking this into account, the presented work demonstrates how a direct-hybrid system must be designed based on a scaled mission profile of a 40-seater aircraft. The fuel cell and battery are configured and sized according to the power demand in different flight phases while considering voltage limits given by the powertrain. The energy requirement from the fuel cell and the battery is calculated for a flight based on a realistic mission profile and different battery and fuel cell configurations are evaluated. By optimizing the battery and fuel cell size, the energy required from the battery was reduced by 57% and the total weight of the fuel cell and battery was reduced by 11%.

Towards a more reliable forecast of ice supersaturation: concept of a one-moment ice-cloud scheme that avoids saturation adjustment

Abstract. A significant share of aviation's climate impact is due to persistent contrails. Thus, avoiding the creation of contrails that exert a warming impact is a crucial step in approaching the goal of sustainable air transportation. For this purpose, a reliable forecast of when and where persistent contrails are expected to form is needed (i.e. a reliable prediction of ice supersaturation). With such a forecast at hand, it would be possible to plan aircraft routes on which the formation of persistent contrails can be avoided. One problem on the way to these forecasts is the current systematic underestimation of the frequency and degree of ice supersaturation at cruise altitudes in numerical weather prediction due to the practice of “saturation adjustment”. In this common parameterisation, the air inside cirrus clouds is assumed to be exactly at ice saturation, while measurement studies have found cirrus clouds to be quite often out of equilibrium. In this study, we propose a new ice-cloud scheme that overcomes saturation adjustment by explicitly modelling the decay of the in-cloud humidity after nucleation, thereby allowing for both in-cloud super- and subsaturation. To achieve this, we introduce the in-cloud humidity as a new prognostic variable and derive the humidity distribution in newly generated cloud parts from a stochastic box model that divides a model grid box into a large number of air parcels and treats them individually. The new scheme is then tested against a parameterisation that uses saturation adjustment, where the stochastic box model serves as a benchmark. It is shown that saturation adjustment underestimates humidity, both shortly after nucleation, when the actual cloud is still highly supersaturated, and also in aged cirrus if the temperature keeps decreasing, as the actual cloud remains in a slightly supersaturated state in this case. The new parameterisation, on the other hand, closely follows the behaviour of the stochastic box model in any considered case. The improvement in comparison with saturation adjustment is largest if slow updraughts occur in relatively clean air in models with a high spatial and temporal resolution. We conclude that our parameterisation is promising but needs further testing in more realistic frameworks.

Effect of Engine Design Parameters on the Climate Impact of Aircraft: A Case Study Based on Short-Medium Range Mission

The climate impact of aviation is considerably different from that of other transport modes. The turbofan engine’s efficiency can be increased by increasing the Operating Pressure Ratio (OPR), bypass ratio (BPR) and Turbine Inlet Temperature (TIT), thereby reducing CO2 and H2O emissions. However, this may have an adverse effect on the secondary emissions, such as NOx, soot, etc. Taking a holistic view in evaluating the climate impact of engine development trends considering all the climate forcers is imperative for design trends in the future. This research investigates the impact of some key engine design parameters on climate. The emission changes due to design variations in the CFM56-5B are estimated using in-house engine performance and emission prediction tools. Accordingly, the changes in the species’ Average Temperature Response for 100 years (ATR100) are analyzed using a climate assessment tool, AirClim. The results show that the overall climate impact increases by 40% when increasing OPR from 25 to 40. Meanwhile, the Twin Annular Premixed Swirler (TAPS-II) combustor reduces the total ATR100 drastically, in the range of 52–58%, due to lean combustion.

Low pressure influence on a direct fuel cell battery hybrid system for aviation

Fuel-cell-based, hydrogen-driven aircraft can significantly reduce the climate impact of aviation but the low ambient pressures at high altitude negatively affect the performance of fuel cells. The influence of low pressures on the behavior of a direct hybrid-system that connects a fuel cell and a battery without a DC/DC converter, is examined and compared to a fuel-cell-only system. Low ambient pressure leads to a reduced fuel cell voltage and power output. The voltage change between maximum voltage and the voltage level at the operational power increases with a decreasing air pressure for both the hybrid-system and the fuel-cell-only system. However, in a direct hybrid, the battery stabilizes the system voltage level and the voltage decrease is significantly smaller for the hybrid-system than for the fuel-cell-only system. At an ambient pressure of 300 mbar, the voltage variation of a 4 kW system is 96% lower for a hybrid-system compared to a fuel-cell-only system. The lower pressure also reduces the power output of the fuel cell. In the direct hybrid the battery contributes a demand related share of power and the contribution from the fuel cell decreases with air pressure as the contribution of the battery rises.

Operational Improvements to Reduce the Climate Impact of Aviation—A Comparative Study from EU Project ClimOP

Aviation significantly contributes to anthropogenic radiative forcing with both CO2 and non-CO2 emissions. In contrast to technical advancements to mitigate the climate impact, operational measures can benefit from short implementation times and thus are expected to be of high relevance in the near future. This study evaluates the climate mitigation potential of nine operational improvements, covering both in-flight and ground operations. For this purpose, an innovative approach is presented to compare the results of measure-specific case studies, despite the wide differences in the underlying modeling assumptions and boundary conditions. To this end, a selection of KPIs is identified to estimate the impact of the studied operational improvements on both climate and the stakeholders of the air transport system. This article presents a comparative method to scale the results of the individual studies to a comparable reference, considering differences in traffic sample size as well as CO2 and non-CO2 climate effects. A quantitative comparison is performed for operational improvements belonging to the same category, i.e., trajectory-related, network-related, and ground-related measures, and a qualitative comparison is carried out among all considered operational improvements. Results show that the in-flight operational improvements are more effective in mitigating the impact on climate with respect to ground operations. However, the latter generally have a weaker impact on the aviation industry and a higher maturity level. Further research could expand this study by assessing the effects of implementation enablers, such as actions at the regulatory level, to facilitate the acceptance of the studied measures in the aviation industry.

Performance Analysis of Resistive Superconducting Fault Current Limiter Using LN2and GHe Cooling

Large-scale electric aircraft is a disruptive technology to address the environmental impact of air travel. Fault current limitation is crucial to realise the safety and reliability of the electric aircraft, in particular for large-scale electric aircraft using DC distribution network. This paper investigates the behavior of the resistive SFCL under different cryogenic cooling systems including liquid nitrogen and helium gas circulation cooling systems for the electric aircraft DC distribution network. Electromagnetic and thermoelectric models were used to predict the characteristics of resistive SFCL. The simulation results demonstrate that it is promising to design resistive SFCL using liquid nitrogen cooling as well as helium gas circulation cooling systems, which offer flexibility for SFCL cryogenic cooling system for electric aircraft applications.

DERIVE AND INTEGRATE SUSTAINABILITY CRITERIA IN DESIGN SPACE EXPLORATION OF ADDITIVE MANUFACTURED COMPONENTS

AbstractAdditive manufacturing has the potential to decrease the climate impact of aviation by providing more light-weight designs. Sustainability is however required to be assessed from a systemic view, including all lifecycle phases, and from a social, ecologic, and economic dimension. This is however challenging in early phase design, where also a large design space need to be explored. A case study is carried out with an aerospace company where two candidate engineering design tools are combined to address this. The integration of these two engineering tools are applied on a Turbine Rear Structure, and shows promising results in enabling a systemic view of sustainability to be integrated and assessed in early phase design space explorations of additive manufactured components. It is recommended that the integration between the two tools is further established and validated.

Predicting the climate impact of aviation for en-route emissions: the algorithmic climate change function submodel ACCF 1.0 of EMAC 2.53

Abstract. Using climate-optimized flight trajectories is one essential measure to reduce aviation's climate impact. Detailed knowledge of temporal and spatial climate sensitivity for aviation emissions in the atmosphere is required to realize such a climate mitigation measure. The algorithmic Climate Change Functions (aCCFs) represent the basis for such purposes. This paper presents the first version of the Algorithmic Climate Change Function submodel (ACCF 1.0) within the European Centre HAMburg general circulation model (ECHAM) and Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model framework. In the ACCF 1.0, we implement a set of aCCFs (version 1.0) to estimate the average temperature response over 20 years (ATR20) resulting from aviation CO2 emissions and non-CO2 impacts, such as NOx emissions (via ozone production and methane destruction), water vapour emissions, and contrail cirrus. While the aCCF concept has been introduced in previous research, here, we publish a consistent set of aCCF formulas in terms of fuel scenario, metric, and efficacy for the first time. In particular, this paper elaborates on contrail aCCF development, which has not been published before. ACCF 1.0 uses the simulated atmospheric conditions at the emission location as input to calculate the ATR20 per unit of fuel burned, per NOx emitted, or per flown kilometre. In this research, we perform quality checks of the ACCF 1.0 outputs in two aspects. Firstly, we compare climatological values calculated by ACCF 1.0 to previous studies. The comparison confirms that in the Northern Hemisphere between 150–300 hPa altitude (flight corridor), the vertical and latitudinal structure of NOx-induced ozone and H2O effects are well represented by the ACCF model output. The NOx-induced methane effects increase towards lower altitudes and higher latitudes, which behaves differently from the existing literature. For contrail cirrus, the climatological pattern of the ACCF model output corresponds with the literature, except that contrail-cirrus aCCF generates values at low altitudes near polar regions, which is caused by the conditions set up for contrail formation. Secondly, we evaluate the reduction of NOx-induced ozone effects through trajectory optimization, employing the tagging chemistry approach (contribution approach to tag species according to their emission categories and to inherit these tags to other species during the subsequent chemical reactions). The simulation results show that climate-optimized trajectories reduce the radiative forcing contribution from aviation NOx-induced ozone compared to cost-optimized trajectories. Finally, we couple the ACCF 1.0 to the air traffic simulation submodel AirTraf version 2.0 and demonstrate the variability of the flight trajectories when the efficacy of individual effects is considered. Based on the 1 d simulation results of a subset of European flights, the total ATR20 of the climate-optimized flights is significantly lower (roughly 50 % less) than that of the cost-optimized flights, with the most considerable contribution from contrail cirrus. The CO2 contribution observed in this study is low compared with the non-CO2 effects, which requires further diagnosis.

Case study on hybrid-electric aircraft designs enabled by an enhanced SUAVE version

Hybridization seems to be a promising way for regional aircraft to reduce the climate impact of aviation in its sector. On the one hand, fully-electric propulsion offers a too limited range while on the other hand, a conventional powertrain cannot offer enough reduction in emissions. In this paper, a case study on hybrid-electric aircraft is performed enabled by an enhanced SUAVE version. A variation on several parameters is carried out for one exemplary hybrid-electric architecture: battery technology level, energy management strategies, hybridization of installed power, cruise speed and altitude. From this study a baseline design, focused mainly on environmental aspects, is selected. The impact of NOX emissions is improved by 83 % compared to the ATR 42, while CO2 has a 5 % benefit without accounting for the net-effect of sustainable aviation fuels which is not part of this study.

A Review on Strategies to Reduce Fuel Consumption in Different Phases of Flight

Abstract: Fuel consumption is a critical aspect of aviation that directly impacts the cost, safety, and environmental impact of air travel. Aircraft require significant amounts of fuel to power their engines and maintain their altitude and speed during flight. Therefore, optimizing fuel consumption is a key priority for airlines, pilots, and aviation engineers. By understanding the factors that affect fuel consumption airlines can develop fuel-efficient flight plans and operational procedures that reduce costs and minimize the environmental impact of air travel. Research on ways to reduce fuel consumption are ongoing and lots of investment and research is required to improve the efficiency and sustainability of air transportation. In this review paper we will be discussing the ways airlines can reduce overall fuel burn in different phases of flight by using certain methods and procedures.

Design Exploration for Sustainable Regional Hybrid-Electric Aircraft: A Study Based on Technology Forecasts

The environmental impact of aviation in terms of noise and pollutant emissions has gained public attention in the last few years. In addition, the foreseen financial benefits of an increased energy efficiency have motivated the transport industry to invest in propulsion alternatives. This work is collocated within the Clean Sky 2 project GENESIS, focused on the environmental sustainability of 50-passenger hybrid-electric aircraft from a life-cycle-based perspective to support the development of a technology roadmap for transitioning towards sustainable and competitive electric aircraft systems. While several studies have already focused on the definition of possible aircraft designs combining several propulsion systems, the novelty of the present work is to consider technology forecasts and more comprehensive indicators in the design phase. These include the performance and emissions on a 200 nmi typical mission, which reflects the most economically attractive range for aircraft in the regional class. The work proposes a complete exploration of three major technology streams for energy storage: batteries, fuel cells, and turbine internal combustion engine generators, also including possible combinations of those technologies. The exploration was carried out through the execution of several designs of experiments aiming at the identification of the most promising solutions in terms of aircraft configuration for three different time horizons: short-term, 2025–2035; medium-term, 2035–2045; and long-term, 2045–2050+. As a result, in the short-term scenario, fuel energy consumption is estimated to be reduced by around 24% with respect to conventional aircraft with the same entry-into-service year thanks to the use of hybrid propulsive systems with lithium batteries. Fuel saving increases to 45% in the medium-term horizon due to the improvement in the energy density of storage systems. By the year 2050, when hydrogen fuel cells are estimated to be mature enough to completely replace kerosene-based engines, the forthcoming hybrid-electric aircraft promise no NOx and CO2 direct emissions, while being approximately 50% heavier than conventional ones.

An audit of the carbon footprint of travel for the Canadian Anesthesiologists' Society International Education Foundation partnerships.

International partnerships have an important role in capacity building in global health, but frequently involve travel and its associated carbon footprint. The environmental impact of global health partnerships has not previously been quantified. We conducted a retrospective internal audit of the environmental impact of air travel for the international education programs of the Canadian Anesthesiology Society's International Education Fund (CASIEF). We compiled a comprehensive list of volunteer travel routes and used the International Civil Aviation Organization Carbon Emissions Calculator, which considers travel distance, passenger numbers, and average operational data for optimized estimates. Comparisons were made with average Canadian household emissions and disability adjusted life years (DALYs) lost from climate change consequences. The total carbon dioxide emitted (CO2-e) for the Rwanda, Ethiopia, and Guyana CASIEF partnerships were 268.2, 60.7, and 52.0 tons, respectively. The DALYs cost of these programs combined is estimated to be as high as 1.1 years of life lost due to the effects of CO2-e. The mean daily carbon cost of the average Rwanda partnership was equivalent to daily emissions of 2.2 Canadians (or 383 Rwandans), for the Guyana partnership was equivalent to 1.6 Canadians (or 7.6 Guyanese people), and for the Ethiopia partnership was equivalent to 2.4 Canadians (or 252 Ethiopian people). Air travel from these CASIEF partnerships resulted in 380.9 tons CO2-e but also enabled 5,601 volunteer days-in-country since 2014. The estimated environmental cost needs to be balanced against the impact of the programs. Regardless, carbon-reduction remains a priority, whether by discouraging premium class travel, organizing longer trips to reduce daily emissions, prioritizing remote support and virtual education, or developing partnerships closer to home.

Climate-Optimised Intermediate Stop Operations: Mitigation Potential and Differences from Fuel-Optimised Configuration

Saving fuel by splitting a flight mission with an intermediate stop for refuelling is described by the concept of intermediate stop operations. This can also be beneficial to the climate impact of aviation, if the flight level and intermediate stop airport are selected accordingly. This study aims to estimate the mitigation potential of an implementation of climate-optimised intermediate stop operations for European long-haul flights and compare it to fuel-optimal operations. For this purpose, fuel consumption and emissions are simulated along four-dimensional trajectories for the selected annual flight plan, and their average temperature response is calculated. A comparison between the reference case and climate-optimised as well as fuel-optimised scenarios shows a significant climate mitigation potential and reveals a shift of trajectories to lower latitudes and altitudes. However, increased flight times and fuel consumption limit implementation from stakeholders’ perspectives.

The Water-Enhanced Turbofan as Enabler for Climate-Neutral Aviation

A significant part of the current aviation climate impact is caused by non-carbon-dioxide emissions, mainly nitrogen oxides (NOx) and contrails. It is, therefore, important to have a holistic view on climate metrics. Today’s conventional, but already well-developed, aero-engines are based on the Joule–Brayton cycle, and leave only limited room for improvement in climate impact. The revolutionary Water-Enhanced Turbofan (WET) concept represents a technical step change addressing all relevant emissions by implementing the Cheng cycle, which combines the gas turbine cycle with a Clausius–Rankine steam cycle. This paper builds upon previous publications regarding the WET concept, and outlines the evolution since then. Promising WET configurations are evaluated according to their ability to reduce global warming potential compared to an evolutionarily advanced turbofan engine. A quantitative approach to estimate reduction of NOx emissions through steam injection is presented. The impact on the creation of contrails is considered using the Schmidt-Appleman criterion. In conclusion, all three climate-relevant emissions can be reduced with the WET concept compared to a technologically similar turbofan in terms of CO2 (up to 10%), NOx (more than 90%), and contrails (more than 50%). The resulting in-flight climate impact can be reduced by more than 40% when using fossil kerosene, paving the way to climate-neutral aviation.

Transport patterns of global aviation NOx and their short-term O3 radiative forcing – a machine learning approach

Abstract. Aviation produces a net climate warming contribution that comprises multiple forcing terms of mixed sign. Aircraft NOx emissions are associated with both warming and cooling terms, with the short-term increase in O3 induced by NOx emissions being the dominant warming effect. The uncertainty associated with the magnitude of this climate forcer is amongst the highest out of all contributors from aviation and is owed to the nonlinearity of the NOx–O3 chemistry and the large dependency of the response on space and time, i.e., on the meteorological condition and background atmospheric composition. This study addresses how transport patterns of emitted NOx and their climate effects vary with respect to regions (North America, South America, Africa, Eurasia and Australasia) and seasons (January–March and July–September in 2014) by employing global-scale simulations. We quantify the climate effects from NOx emissions released at a representative aircraft cruise altitude of 250 hPa (∼10 400 m) in terms of radiative forcing resulting from their induced short-term contributions to O3. The emitted NOx is transported with Lagrangian air parcels within the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. To identify the main global transport patterns and associated climate impacts of the 14 000 simulated air parcel trajectories, the unsupervised QuickBundles clustering algorithm is adapted and applied. Results reveal a strong seasonal dependence of the contribution of NOx emissions to O3. For most regions, an inverse relationship is found between an air parcel's downward transport and its mean contribution to O3. NOx emitted in the northern regions (North America and Eurasia) experience the longest residence times in the upper midlatitudes (40 %–45 % of their lifetime), while those beginning in the south (South America, Africa and Australasia) remain mostly in the Tropics (45 %–50 % of their lifetime). Due to elevated O3 sensitivities, emissions in Australasia induce the highest overall radiative forcing, attaining values that are larger by factors of 2.7 and 1.2 relative to Eurasia during January and July, respectively. The location of the emissions does not necessarily correspond to the region that will be most affected – for instance, NOx over North America in July will induce the largest radiative forcing in Europe. Overall, this study highlights the spatially and temporally heterogeneous nature of the NOx–O3 chemistry from a global perspective, which needs to be accounted for in efforts to minimize aviation's climate impact, given the sector's resilient growth.

The perceived value of environmental sustainability for consumers in the air travel industry: A choice-based conjoint analysis

By 2050, aviation emissions are forecasted to account for 25% of the global carbon budget. Thus, in addition to airlines’ sustainability efforts, individual consumer action is needed in order to reduce the environmental impact of air travel. The purpose of this paper is to investigate to what extent consumers value environmental sustainability when selecting flights in terms of the trade-off between cost, time, comfort, and CO2 emissions. Hence, a choice-based conjoint survey was conducted to understand the monetary, temporal, and comfort trade-offs consumers are willing to make for a reduction in CO2 emissions in both short-haul and long-haul flights. The 426 collected responses were analysed using conditional logistic regressions. The results indicate that air travellers are willing to pay more (6.7–21.2 €/100 kg) or travel longer (13–41 minutes/100 kg) to reduce the environmental impact of their trip. Moreover, displaying CO2 emissions as a percentage of an individual’s annual carbon budget increased air travellers’ perceived monetary and temporal value of environmental sustainability, to 11.8–26.3 €/100 kg and 22–65 minutes/100 kg respectively.